Field of the Invention
The present invention relates to a container inspection device and a container inspection method for inspecting containers or its secondary packaging units logically corresponding thereto like beverage crates and bundles or pallets. The container inspection device and the container inspection method may be employed in a container treatment plant, for example, in which the containers are inspected for faults, defects, etc.
Description of the Prior Art
DE 100 17 126 C1 shows a method and a device for optically examining transparent containers. The device for performing the method comprises a LED lighting screen having a plurality LEDs which can be activated individually or in groups. The LED lighting screen is positioned adjacent to a stream formed from a row of transparent containers positioned one after the other, a container stream. When the containers are illuminated by the LED lighting screen, a picture or image of the container can be taken to perform the optical examination of the containers.
An inspection device comprises, thus, an illumination, an optical recording unit and an image evaluating unit. The recording unit and the image evaluating unit may be realized in the same apparatus, like for example in so-called vision-sensors or intelligent cameras, but may also be implemented separately, like for example in a camera and a separate image evaluating unit.
For the illumination of the inspection device, different kinds of technical light fixtures are used in general in the field of inspection. The illumination can be implemented as permanent light or switched light or flashed light. Illuminating with permanent light is understood in this context as comprising a luminous time TON of 1 second to ∞. When illuminating with switched light, the luminous time TON has a value of approximately 150 μs up to approximately 2 s. When illuminating with flashed light, the luminous time TON has a value of approximately 1 μs to 400 μs. The transitions are fluent. In the other time, that is the non-luminous time, the illumination is switched off. This time in which it is not illuminated is referenced as switched-off time TOFF.
The inspection of containers, in particular the inspection of containers during the movement in container treatment plants for filling containers, is preferably implemented by flashed light. This is at the same time the most intricate illumination. In case the inspection task allows it, also a switched illumination or a permanent light may be employed. Flashed or switched illuminations can comprise an own energy storage to provide an energy amount which is big enough for the duration of the luminous time TON. In the following, flash illuminations are mentioned only, however, the explanations are valid for switched illuminations in the same way.
The initiating of an illumination is effected by a trigger signal which releases a predefined flash duration or is controlled by the signal length.
As a result, the illumination needs at least the following contacts for the energy supply, a flashed or switched illumination, and additionally a trigger-signal or a switch-on-signal (TON-signal) for initiating the flashed or switched illumination.
In the evaluating unit is used a shutter for the recording unit which may be implemented as a 1D-, 2D- or 3D-camera, wherein the shutter is open for a predetermined shutter time TS and releases a recording sensor.
Only the time intersection of the shutter time TS and the illuminating time TON actually acts on the recording sensor and generates an image with the effective illuminating time TS. The intensity of the resulting image is the integral of the light intensity in the recording sensor over the effective illuminating time TB. Images of the same intensity can be achieved only, if the intensity of the illumination and the effective exposure time TB are constant.
In the technical implementation, either the luminous time TON is set so that the shutter time TS is always inside the luminous time TON or that the luminous time TON is always inside the shutter time TS. However, the luminous time TON should not be lengthened arbitrarily, since the advantages of the luminous time TON which is to be actually chosen, are lost in this case. In the case of the other way round, also the shutter time TS should not be lengthened arbitrarily, since in this case the recording sensor is sensitive to extraneous light, like environment light or light flashes, from other inspection units and can confuse the subsequent evaluation.
To avoid the mentioned disadvantages, the illumination has to be synchronized with the recording unit. In the prior art, the synchronization is achieved by a common trigger line or the recording unit controls the illumination by a digital output. It is further possible that the illumination controls the recording unit.
A synchronization of a clock of the recording unit and a clock of the illumination can be made for example by a computer network on which runs an established time protocol like SNTP or NTP. However, a computer network cannot guarantee, that a communication packet reaches the recording unit and the illumination as the parties or rather nodes of the synchronization within a predefined time. The predefined time derives itself for example from the field of view of the recording unit as well as the reaction time for recording after the detection of the container. The smaller the field of view, the shorter is the path between the detection of the container and the location of the record. The time for a transport of the container along the path is calculated from the transport velocity of the container treatment plant, which accounts in a stretch blow molding machine up to 8 m/s. A rotary encoder signal is relevant for the reaction time. It is examined with the rotary encoder signal approximately every 100 μs to 10 ms, typically every 0.2 to 5 ms, whether the container has actually passed the path between the detection of the container and the location of the recording. The container detection signal and the rotary encoder signal are stimuli for the decision, when a record shall be initiated by the recording unit. Because of the short reaction time resulting for the mentioned conditions for a container treatment plant and therewith the predetermined time, the computer network is not applicable for the timely, synchronized initiation of the exposure and flash time and therewith for the required synchronization.
A further disadvantage of hitherto solutions in a container inspection device for a container treatment plant is given by the intricate cabling. For a container treatment plant, the illumination has to be reconfigured frequently since the lamp color has to be adapted to the container material, luminous segments have to be adapted to the container geometry, etc. In these cases, a supply cable with trigger signal and further lines have to be connected to the illumination.
As regards the trigger line, there is also the problem that a line which is installed unfavorable can couple in disturbances and can uncontrollably initiate a flash illumination. Wrongly, uncontrollably initiated triggers use energy of the energy storage of the illumination inadvertently. If the energy storage is not loaded sufficiently, a necessary flash cannot be performed with the complete brightness. As a result, the brightness fluctuates in the recorded image, in the worst case, the image is too dark. Therewith, the burden of the cabling increases, since power guiding (motor) lines are to be installed separately from the trigger line.
A further problem lies in that a plurality of fast output contacts are required as regards a container inspection device. Not only the stimuli have to be read in in a higher ranking system, but also the output contacts have to be provided. Therewith, the costs of the container treatment plant increase.
A further disadvantage lies in that the cabling topology has to be known in advance. Possible changes or additions require a change of the cabling plan. Example: recording unit A and B use the same illumination. The recording units A, B act independent from each other. The output contacts of both recording units A, B control the illumination. Diodes are used for decoupling. In case it is to be changed per worked product between a through-light-illumination C and incident illumination D, the synchronization between the cameras and the illuminations is very intricate. A solution may be additional AND-gates in the illumination path. However, the trigger possibilities have to be known also here a priori.